Thursday, May 9, 2013

New paper finds upper limit of sea level rise from Antarctic ice sheet is about 70% less than IPCC upper limit

A paper published today in the Journal of Geophysical Research - Solid Earth finds "The new upper bound [upper limit] to sea-level rise from the Antarctic ice sheet (AIS) averaged over the time span 2003 - 2012 is about 0.16 ± 0.09 mm/yr." At this rate, this is equivalent to an upper limit of about one-half inch sea level contribution by the year 2100, and is about 70% less than the IPCC AR4 upper limit estimate of sea level contribution from the Antarctic ice sheet of 0.21 ± 0.35 mm/yr [upper limit 0.56 mm/yr] from 1993-2003. Related: NOAA 2012 report finds sea levels rising at less than half the rate claimed by the IPCC

Abstract: Antarctic volume changes during the past 21 thousand years are smaller than previously thought and here we construct an ice sheet history that drives a forward model prediction of glacial isostatic adjustment (GIA) gravity signal. The new model, in turn, should give predictions constrained with recent uplift data. The impact of the GIA signal on a Gravity Recovery and Climate Experiment (GRACE) Antarctic mass balance estimate, depends on the specific GRACE analysis method used. For the method described in this paper, the GIA contribution to the apparent surface mass change is re-evaluated to be +55 ± 13 Gt/yr by considering a revised ice history model and a parameter search for vertical motion predictions that best-fit the GPS observations at 18 high-quality stations. Although the GIA model spans a range of possible earth rheological structure values, the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity, nor for a preferred lithospheric thickness. GRACE monthly solutions from CSR-RL04 release time series from Jan. 2003 through the beginning of Jan. 2012, uncorrected for GIA, yield an ice mass rate of +2.9 ± 29 Gt/yr. The new GIA correction increases the solved-for ice mass imbalance of Antarctica to −57 ± 34 Gt/yr. The revised GIA correction is smaller than past GRACE estimates by about 50 to 90 Gt/yr. The new upper bound to sea-level rise from the Antarctic ice sheet (AIS) averaged over the time span 2003.0 - 2012.0 is about 0.16 ± 0.09 mm/yr.